#34325: PercentRank confusion
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Reporter: dvg | Owner: nobody
Type: Uncategorized | Status: new
Component: Documentation | Version: 4.1
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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The [https://docs.djangoproject.com/en/4.1/ref/models/database-
functions/#percentrank documentation for the PercentRank window function]
says:
Computes the '''''percentile rank''''' of the rows in the frame clause.
This computation is equivalent to evaluating:
{{{
(rank - 1) / (total rows - 1)
}}}
(my emphasis)
However, I'm not so sure
"[https://en.wikipedia.org/w/index.php?title=Percentile&oldid=1114275310
percentile] rank" is the correct term.
If you look up the (statistical) term "percentile rank" online, you'll
find various definitions,
[https://en.wikipedia.org/w/index.php?title=Percentile_rank&oldid=1136815121
ranging from]
{{{
(CF - 0.5 * F) / N
}}}
where CF—the cumulative frequency—is the count of all scores less than
or equal to the score of interest, F is the frequency for the score of
interest, and N is the number of scores in the distribution.
[https://www.geo.fu-berlin.de/en/v/soga/Basics-of-statistics/Descriptive-
Statistics/Measures-of-Position/Percentiles-and-Percentile-Rank/index.html
to something like]
{{{
<number of values less than the score of interest> / <total number of
values in the data set>
}}}
However, none exactly matches the definition in the Django docs.
Note also that the documentation for the `percent_rank` function in the
[https://www.sqlite.org/windowfunctions.html#built_in_window_functions
SQLite] and [https://www.postgresql.org/docs/15/functions-window.html
PostgreSQL] database backends does '''not''' mention "percentile rank".
Instead, they use the term "relative rank."
To prevent confusion, wouldn't it be better to use the same terminology as
the database backends?
--
Ticket URL: <https://code.djangoproject.com/ticket/34325>
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